| Summary: | The signaling pathways induced by <i>Pseudomonas putida</i> in rice plants at the early plant–rhizobacteria interaction stages, with and without inoculation of <i>Xanthomonas oryzae</i> pv. <i>oryzae</i>, were studied. In the absence of pathogen, <i>P. putida</i> reduced ethylene (ET) production, and promoted root and stem elongation. Interestingly, gene <i>OsHDA702</i>, which plays an important role in root formation, was found significantly up-regulated in the presence of the rhizobacterium. Although <i>X. oryzae</i> pv. <i>oryzae</i> inoculation enhanced ET production in rice plants, <i>P. putida</i> treatment repressed ET-, jasmonic acid (JA)- and salicylic acid (SA)-mediated defense pathways, and induced the biosynthesis of abscisic acid (ABA), and the overexpression of <i>OsHDA705</i> and some pathogenesis-related proteins (PRs), which in turn increased the susceptibility of the rice plants against the pathogen. Collectively, this is the first work on the defense signaling induced by plant growth-promoting rhizobacteria in plants at the early interaction stages, and suggests that rhizobacteria stimulate an alternative defense mechanism in plants based on ABA accumulation and <i>OsHDA705</i> signaling.
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